The deployment of an insect “refuge” is an important part of insect resistance management (IRM) for transgenic pest resistant crops. Governmental agencies, such as the Environmental Protection Agency in the United States, require that transgenic insect resistant crops be planted along with or along side a refuge crop.
Corn (Zea mays) is an important crop in many areas of the world, and the methods of biotechnology have been applied to this crop in order to produce corn with desirable traits. The expression of an insect resistance or herbicide tolerance transgene in a plant can confer the desirable traits of insect resistance and/or herbicide tolerance on the plant, but expression of such transgenes may be influenced by many different factors including the orientation and composition of the cassettes driving expression of the individual genes transferred to the plant chromosome, and the chromosomal location and the genomic result of the transgene insertion. For example, there can be variation in the level and pattern of transgene expression among individual events that are otherwise identical except for the chromosomal insertion site of the transgene. There may also be undesirable phenotypic or agronomic differences between some events. Therefore, it is often necessary to produce and analyze a large number of individual plant transformation events in order to select an event having superior properties relative to the desirable trait and the optimal phenotypic and agricultural characteristics necessary to make it suitable for commercial purposes. Such selection often requires extensive molecular characterization as well as greenhouse and field trials with many events over multiple years, in multiple locations, and under a variety of conditions so that a significant amount of agronomic, phenotypic, and molecular data may be collected. The resulting data and observations must then be analyzed by teams of scientists and agronomists with the goal of selecting a commercially suitable event. Once selected, such an event may then be used for introgressing the desirable trait into other genetic backgrounds using plant breeding methods, and thus producing a number of different crop varieties that contain the desirable trait and are suitably adapted to specific local growing conditions.
To make a transgenic plant containing a single transformation event, a portion of a recombinant DNA construct is transferred into the genome of a corn cell, and the corn cell is subsequently grown into a plant. A corn cell into which the event is initially transferred is regenerated to produce the R0 generation. The R0 plant and progeny plants from the R0 plant can be tested for any desired trait(s), but the effectiveness of the event can be impacted by cis and/or trans factors relative to the integration site in the transformation event. The phenotype conferred by the event can also be impacted by the size and design of the DNA construct, which can vary by the combination of genetic elements in an expression cassette, number of transgenes, number of expression cassettes, and configuration of such elements and such cassettes. Identifying an event with desirable traits can be further complicated by factors such as plant developmental, diurnal, temporal, or spatial patterns of transgene expression; or by extrinsic factors, e.g., environmental plant growth conditions, water availability, nitrogen availability, heat, or stress. Thus, the ability to obtain an event conferring a desirable set of phenotypic traits is not readily predictable.